Correct Option: (C) $E_{\text{ext}} > E_{\text{cell}}$

Step 1 (Governing Principle): [0.5 Mark]

A galvanic cell converts chemical energy into electrical energy. The direction of current flow and the nature of the cell reaction are governed by the relationship between the external opposing potential ($E_{\text{ext}}$) and the cell potential ($E_{\text{cell}}$). According to the NCERT textbook, the cell functions as an electrolytic cell when the external potential is increased beyond the potential of the galvanic cell.

Step 2 (Step-by-Step Logical Deduction): [0.25 Mark]

• If $E_{\text{ext}} < E_{\text{cell}}$: Electrons flow from anode to cathode; the cell acts as a galvanic cell.
• If $E_{\text{ext}} = E_{\text{cell}}$: No current flows; the reaction is at equilibrium.
• If $E_{\text{ext}} > E_{\text{cell}}$: The external potential overcomes the cell potential, forcing electrons to flow in the opposite direction (from cathode to anode). This reverses the chemical reaction, effectively turning the galvanic cell into an electrolytic cell.

Step 3 (Final Concluded Answer): [0.25 Mark]

Therefore, the condition for a galvanic cell to function as an electrolytic cell is:

💡 EL10 Concept Insight: Think of a galvanic cell like a ball rolling down a hill; if you push it harder from the bottom (the external force) than it is rolling down, you force the ball to go back up the hill instead. Similarly, applying a higher external voltage forces the electricity to flow backward, turning the battery into a charger!